Contemporary interactive surfaces generally treat finger touches as a single class of input. However, this is a gross simplification—fingers are diverse appendages, both in their motor capabilities and their anatomical composition. Supporting additional dimensions of finger input have largely been ignored because instrumenting the user with active or passive components is invasive.
At present, in order for a finger to perform different operations at a single point in space on a touch screen, it must be overloaded (e.g., in time or space). Most common is a tap-and-hold period, or chording of the fingers (e.g., two-finger-tap for right click). This can trigger a transient contextual menu, which allows a user to select one of several actions. An alternative to finger overloading is breaking function out into one or more buttons. For example, there is a scheme in which one button is for minimizing a window and another button is for closing it. However, this is problematic for mobile devices with limited screen real estate.
Currently, touch screens do not distinguish between different types of finger contacts. For example, touching with the tip of the finger and touching with the knuckle are treated the same. As such, all finger touches have the same interactive outcome. Also, currently, touch screen interfaces generally pass input events (e.g. finger touches) directly through to running applications. For example, a finger press on an application icon that is visible on the touchscreen launches it. As such, all finger touches have interactions with only one interaction layer, for example, with the layer of running application(s) that has (have) software buttons or other widgets, or icons that are visible on the touch screen.